The invention relates to the field of hydraulic dampers, more particularly to hydraulic suspension dampers of a motor vehicle. BACKGROUND OF THE INVENTION The invention relates to the damping at the end of the race of such dampers.
A damper in the automotive field provides a number of functions, including the cash register, the behavior of the vehicle and ensure a good level of comfort to the occupants of the vehicle. The thrust and trigger stops are used to limit the wheel stroke. Commonly, these stops generate a level of effort depending on the position of the damper. The more one enters the stop, the greater the effort generated by the stop is important. In order to limit the forces entering the box, it is possible to use hydraulic stops which generate damping forces which are functions of the position and the speed of displacement of the damper rod. Patent document published FR 2 902 850 A1 discloses a hydraulic abutment device for shock absorber, such as a suspension damper of a motor vehicle. The abutment device essentially comprises a piston connected to a rod and sealingly slidable in a cylinder. This comprises a closed bottom and a series of orifices in its side wall, so that the piston, as it moves in the cylinder towards the bottom thereof, moves along these orifices. During this movement, the piston will gradually limit the number of orifices used to evacuate the fluid repelled by the piston. The fluid is thus pushed back from the compression chamber via these orifices to a compensation chamber disposed around the cylinder. The damping of the movement will then intensify gradually. The device can also be adjustable from outside the damper. Indeed, the stop device may comprise a cylindrical wall enclosing the cylinder in which the piston slides. This wall comprises orifices corresponding essentially to those of the cylinder. It is rotatably mounted around the cylinder so that its angular position can be changed. The rotational displacement of this wall thus makes it possible to modulate the passage section of the orifices, and thus to modify the damping characteristic of the hydraulic abutment. This device is interesting in that it can be implemented directly at the main piston of a suspension damper. However, it requires complex and expensive arrangements; it is moreover quite bulky, in particular in the case of an independent abutment associated with a damper, that is to say where the piston of the hydraulic abutment is distinct from that of the damper.
The object of the invention is to provide a hydraulic abutment, particularly for a hydraulic damper, which overcomes at least one of the drawbacks of the above-mentioned state of the art. More particularly, the invention aims to provide a hydraulic damper with damping means at the end of stroke that are effective, compact and economical.
The subject of the invention is a hydraulic damper, in particular for a motor vehicle suspension, comprising: a cylindrical envelope containing a fluid; a piston slidably mounted in the cylindrical envelope and comprising at least one orifice for the fluid; a rod connected to the piston; damping means at the end of the sliding stroke of the piston in the cylindrical envelope; remarkable in that the damping means comprise a rotary valve in contact with the piston, adapted to modulate the passage section of the or at least one of the orifices of the piston; means for rotating the valve with respect to the piston as a function of the sliding position of the piston in the cylindrical envelope. The piston may comprise means for restricting the passage section of the orifices, distinct from the valve and designed to provide a damping function outside the end-of-stroke zone. The damping function at the end of the stroke can be in "attack", that is to say when the rod and the piston sink or enter the cylindrical envelope but also in "relaxation", that is to say that is, when the stem comes out of the cylindrical envelope. The means of rotation of the valve with respect to the piston as a function of the sliding position of the piston in the cylindrical envelope may take several forms. According to an advantageous embodiment of the invention, the rod is a hollow rod and the means of rotation of the valve relative to the piston comprise an indexed rod slidably mounted in the hollow rod and extending outside the hollow rod, so to be able to come into contact with a bottom wall of the cylindrical envelope, the indexed rod being indexed in rotation with the hollow rod and the valve. The bottom wall may be at each of the two ends of the cylindrical envelope, namely at a first end through which the hollow stem extends and at a second end opposite to the first.
According to an advantageous embodiment of the invention, the indexed rod is connected in rotation with the hollow rod and comprises on its outer surface at least one helical groove cooperating with the valve for its rotation as a function of the driving position of the stem indexed in the hollow stem. According to an advantageous embodiment of the invention, the indexed rod comprises a first portion slidably housed in the hollow rod and connected in rotation therewith and a second portion comprising the helical groove or grooves. According to an advantageous embodiment of the invention, the damping means comprise resilient biasing means capable of pulling out the indexed rod from the hollow rod when the hollow rod and the piston move away from the bottom wall of the envelope. cylindrical. According to an advantageous embodiment of the invention, the elastic return means comprise a compression spring housed in the hollow rod and exerting a force on the indexed rod. According to an advantageous embodiment of the invention, the valve is a disk provided with at least one orifice configured to be able to modulate the passage section of the or at least one of the orifices of the piston. According to an advantageous embodiment of the invention, the valve is linked in translation to the piston, the valve being preferably housed in a generally circular cavity of the piston. The valve may however be free to slide axially relative to the piston on a limited stroke. This allows the piston valve to detach during a reverse movement to that of the cushioned movement at the end of the stroke. According to an advantageous embodiment of the invention, the valve is disposed on the face of the piston which is directed towards the damped end position. The invention also relates to a motor vehicle comprising a structure, wheels and suspension means between the wheels and the structure, the suspension means comprising at least one hydraulic damper, remarkable in that the or the hydraulic dampers are in accordance to the invention. The measures of the invention are interesting in that they make it possible to achieve a hydraulic stop function in a damper, and this with a limited number of parts. Indeed, the hollow stem and the piston are in principle still part of a conventional damper. To achieve the hydraulic stop function according to the invention, it is then essentially necessary to provide a suitable section at the inner surface of the hollow rod, to slightly modify the piston and to provide the indexed rod and the valve. Other features and advantages of the present invention will be better understood with the help of the description and the drawings among which: FIG. 1 is a schematic perspective view of a damper according to the invention; - Figure 2 is a longitudinal sectional view of the piston and a portion of the rod of the damper of Figure 2; FIG. 3 is a perspective view of the lower face of the piston of the damper of FIGS. 1 and 2; FIG. 4 is a first view in transparency of the bottom of the shock absorber of FIGS. 1 to 3, at the beginning of the gradual end-of-stroke damping; FIG. 5 is a second view in transparency of the bottom of the damper of FIGS. 1 to 3, at the beginning of progressive damping zone at the end of the stroke; - Figure 6 is a bottom view of the piston and the rotary valve in an angular position where it reduces the passage section for the fluid; - Figure 7 is a sectional view of the piston and the rotary valve in an angular position where it reduces the passage section for the fluid. Figures 1 to 7 are different views illustrating an embodiment of the invention. FIG. 1 is a schematic view in transparency of a damper 2 essentially comprising a generally cylindrical casing 4, a piston 6 slidably mounted in the cylindrical casing 4 and a rod 8 connected to the piston 4. The piston 6 comprises an indexed rod 10 projecting from the rod 8 and directed towards the bottom 5 of the cylindrical envelope. The cylindrical envelope is filled with a fluid, preferably an incompressible fluid such as oil. The rod 8 is intended to be connected at its free end to a first element such as the structure of a vehicle and the cylindrical envelope 4 is intended to be mechanically connected to a second element such as the wheel hub of a vehicle . The displacements of the wheel with respect to the structure of the vehicle during its displacement modify the sizes of the two chambers delimited by the piston 6 in the cylindrical envelope 4. They thus force a displacement of the oil contained in the cylindrical envelope 4 to the other through holes (not shown in Figure 1) in the piston 6. It should be noted that the latter may comprise a stack of flexible valves cooperating with the orifices of the piston to ensure a desired amortization on the main work area of his race. Such measurements are well known per se to those skilled in the art and will therefore not be detailed. FIG. 2 is a sectional view of the piston of the damper of FIG. 1 and FIG. 3 is a view of the face of the piston oriented towards the indexed rod 10. It can be seen that the rod 8 connected to the piston is hollow and that the indexed rod 10 is slidably mounted inside the rod 8. It can also be observed that the piston comprises on its side facing the side of the indexed rod, a valve 14 of generally circular shape, in the manner of a disc. This valve 14 comprises a series 25 orifices 16 substantially corresponding to the orifices 12 of the piston, so as not to substantially modify their passage section when the valve is disposed with its orifices opposite the orifices 12 of the piston. The rod 10 is said indexed to the extent that its displacement relative to the rod 8 and the valve 14 will cause the rotation of the latter relative to the piston. In this case, the indexed rod 10 comprises a first portion sliding in the hollow rod 8 and connected in rotation therewith. To do this, the first portion 20 may have a non-circular outer surface, substantially corresponding to the outer surface of the hollow rod 8. For example, the first portion 20 of the indexed rod 10 and the inner surface of the rod hollow may have one or more grooves oriented in the axial direction, these grooves ensuring a rotational connection between the two rods while allowing their relative axial sliding. The indexed rod 10 comprises a second portion corresponding essentially to the remainder of the rod as illustrated in FIG. 2, this second portion comprising on its outer surface at least one helical groove 18. This groove cooperates with a lug (not visible) of the valve 14 so as to form a connection in rotation between the indexed rod 10 and the valve 14, this connection, however, allowing the rod 10 to slide relative to the valve 14. As will be detailed below, the pitch of the or helical grooves is very large. In other words, the angular variation of the groove 18 changes little with respect to the position its axial position along the rod 10. The reason is that the valve undergoes a small amplitude of rotation on the total stroke of the rod 10 By way of example, the angular travel of the valve may be between 1 ° and 20 °, preferably between 5 ° and 15 ° for an axial stroke of the rod of between 10 mm and 100 mm, preferably between 15 mm and 80 mm, more preferentially between 20mm and 70mm. It should be noted, however, that these values are examples of values, which may vary and deviate from the examples mentioned above, in particular according to the application in question. FIGS. 4 and 5 illustrate, in transparency, the lower part of the damper of the preceding figures, when the piston is moving closer to its end-of-travel position against the bottom 22 of the cylindrical envelope 4, at a position where begins the hydraulic damping of end of race. Indeed, the indexed rod 10 has come into contact with the bottom 22 of the cylindrical casing 4. In this position, the valve 14 in position where its orifices are opposite the orifices 12 of the piston 6 and generates no damping additional to that generated by the orifices 12 and the stacks of flexible claps (not shown). When the piston moves down further with respect to the position illustrated in FIGS. 4 and 5, the indexed rod 10 slides in the hollow rod 8 and causes the valve 14 to rotate relative to the piston 6. This situation is illustrated in FIGS. it can be observed that the orifices 16 of the valve 14 are offset relative to the orifices 12 of the piston and thus limit their equivalent section. The progressive throttling achieved by the displacement of the valve generates a significant pressure difference between the face of the valve which is in the compression chamber and its opposite face against the piston, the pressure on the face in the compression chamber being greater than that on the opposite side. As a result, the valve is naturally pressed against the piston in this damping phase at the end of the race. However, means can be provided to keep it in place. More particularly, the valve is housed in a recess-shaped cavity on the face of the piston directed towards the compression chamber. A circlip (not shown) housed in an internal groove of the cavity may, for example, ensure the maintenance of the valve 14 in this cavity. The movement of movement of the piston from its end position is thus hydraulically braked in a progressive manner. The orifices 16 of the valve and the configuration of the groove or grooves may be sized to ensure the desired damping characteristic. This can be very high at the end of the race, so as to avoid tailgating of the damper. During a detent movement, that is to say a relative movement between the piston and the cylindrical casing, which is opposite to the compression movement just described, a spring (not shown) disposed in the hollow rod and exerting an elastic force on the indexed rod 10 will gradually move said rod in an output direction thereof so as to move the valve 14 in rotation in opposite direction to a position where the end of the rod no longer touches the bottom of the cylindrical casing and the orifices 12 of the piston return to their initial section. The valve 14 may optionally be movable in translation over a reduced stroke, this stroke being able for example to correspond to a portion of the depth of the cavity of the piston in which the valve is housed. Such a measurement would then allow detachment of the valve 14 relative to the piston and thus a rapid increase in the passage section, which can correspond essentially to that of the orifices 12 of the piston 6.
It should be noted that the damping force of the hydraulic stop that has just been described is a function of the speed of movement of the piston relative to the cylindrical envelope. This means that the damping will be all the more important as the sliding speed is large and vice versa. In the context of a motor vehicle suspension damper, it may be useful to provide in addition to this hydraulic stop, an elastic mechanical stop, particularly for rolling situations where the sliding speed is low and the damper is in large settling pattern in steady state. This is particularly the case when the shock absorbers of the outer wheels of a vehicle traveling on a roundabout.